1. Field of the Invention
The present invention is generally related to a hydraulically assisted steering system for a marine vessel and, more particularly, to a method for utilizing a hydraulic pump and associated electric motor in an efficient way which can have the effect of allowing smaller capacity alternators than would otherwise have to be used in conjunction with the hydraulically assisted steering system.
2. Description of the Prior Art
Various types of hydraulic steering systems are known to those skilled in the art for use in conjunction with marine vessels and, more particularly, in conjunction with pleasure craft.
U.S. Pat. No. 6,715,438, which issued to Hundertmark on Apr. 6, 2004, describes a tiller operated power assist marine steering system. The tiller is preferably coupled to the outboard motor or other steering element of a watercraft such that movement of the tiller in a first manner imposes manually generated steering forces on the steering element and that operation of the tiller in a second manner imposes power assist steering forces on the steering element.
U.S. patent application Ser. No. 10/702,560, which was filed on Nov. 7, 2003 by Watanabe et al., describes a power steering device for a boat with an outboard motor. To provide a power steering device which helps to realize easy drive with small steering force without taking waterproofness into consideration, a gear device is provided for driving a link mechanism for turning and steering an outboard motor main body at the rear of the boat body through a cable by a steering wheel. A steering torque input to the gear device by the steering wheel is detected by a torque sensor to assist drive the gear device in the steering direction by an electric motor, a helical pinion, and a helical wheel.
U.S. Pat. No. 6,598,553, which issued to Hundertmark on Jul. 29, 2003, describes a power assist marine steering system. The system includes a hydraulically actuated steering cylinder assembly and a helm. The helm has a high pressure port being coupled to a fluid pressure source, a return port coupled to the reservoir, and a metering port coupled to a second chamber of the steering cylinder.
U.S. Pat. No. 5,340,341, which issued to Yoshimura on Aug. 23, 1994, describes a power assisting mechanism for a marine propulsion unit. The steering and gear shift system comprises a single source of hydraulic power, a steering device, a gear shift member, steering and gear shift control mechanism connected to their respective members and first and second assist devices connected to the gear shift and steering control mechanism for power assist. A single substantially constant output hydraulic pump supplies an essentially constant level of fluid power for the first and second power assist devices to assist the operator in controlling the steering and gear shift controls.
U.S. Pat. No. 5,376,029, which issued to Entringer et al. on Dec. 27, 1994, discloses a control valve for a pressurized fluid operated system, such as a marine power steering system, and includes a housing having an inlet and at least one outlet with one or more work ports located therebetween. Pressurized fluid is supplied to the inlet, and a spool member is mounted within the housing for controlling the supply of pressurized fluid to a work performing system, such as the extendable and retractable rod of a hydraulic cylinder assembly. The spool member includes structure for blocking the one or more work ports when the spool member is in its neutral position when it is desired not to operate the system. This prevents the cylinder from being exposed to reservoir fluid when the spool member is in its neutral position.
U.S. Pat. No. 5,427,555, which issued to Merten on Jun. 27, 1995, describes a power steering system. The system is interposed between the steering helm and the propulsion unit and mounted remote from the propulsion unit, and further is hydraulically actuated in response to operative movement at the steering helm. A gear drive means, actuated in response to steering actuation at the helm, is operably connected to power steering assist means, comprising a hydraulic cylinder piston assembly and hydraulic fluid source.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
When a hydraulically assisted steering system is added, as an after-market component, to an existing marine propulsion system, the provision of hydraulic power for the system can require a level of electrical power that is greater than the magnitude of electrical power which can be easily generated by the existing alternator of the marine propulsion system. In other words, an existing alternator provided for an outboard motor may not have the capacity needed to generate the additional electric power necessary to operate a hydraulic pump and motor that provides hydraulic pressure for the hydraulically assisted steering system which is added, as a retrofit improvement, to the marine propulsion system.
Known types of retrofit hydraulically assisted steering systems typically operate in one of two common ways. In some systems, the hydraulic pump is constantly driven by an electric motor to generate hydraulic pressure continually, with excess hydraulic fluid being recirculated to a hydraulic fluid reservoir. Other systems utilize a pressure accumulator that is pressurized by the motor driven pump whenever the pressure within the accumulator falls below a preselected magnitude. As the pressure is used by the hydraulic steering system, the pressure in the accumulator decreases. When the pressure in the accumulator is reduced to a preselected minimum magnitude, a switch causes the motor driven pump to be activated to increase the pressure within the accumulator.
It would be beneficial if a retrofit hydraulically assisted steering system could be provided which does not require an accumulator and does not continually operate a motor driven pump which requires excessive electric power which is beyond the normal capacity of the alternator provided in the outboard motor.